Local area networks (LANs) have grown tremendously in the last few years and, leading the way in the growth of LANs is the Ethernet type LAN. Ethernet was first developed in the mid 1970's. By the early 1980's, the Institute of Electrical and Electronic Engineers (IEEE) developed a standard for Ethernet designated as IEEE 802.3, which has been universally adopted by the network industry. From the early 1980's until the present, the IEEE 802.3 standard has undergone many revisions, including the addition of new features such as switched Ethernet, Fast Ethernet, Gigabit Ethernet and the like. Recently, the IEEE has adopted a new addition to the IEEE 802.3 standard, 802.3af, related to the transmitting of power over Ethernet transmission lines.
Specifically, the 802.3af addition, referred to commonly as “Power over Ethernet”, involves delivering 48 volts of AC power over unshielded twisted-pair wiring. Power over Ethernet provides for power to be supplied over existing Ethernet infrastructure; i.e., existing cable, horizontal and patch cables, patch-panels, outlets; and connecting hardware are implemented.
Traditionally, network devices, such as IP phones, wireless LAN access points, laptop computers and the like, have required both an Ethernet connection and an AC electrical connection. Given the increasing number of LAN devices in corporations, wiring AC connections for each of them is a costly task. The 802.3af specification eliminates the need for additional outlets and the labor cost incurred from contracting electricians to install them.
Additionally, Power over Ethernet technology supports a point-to-multipoint power distribution architecture, parallel to the data network. This functionality allows network managers to implement a single uninterruptible power supply (UPS) at the network core to back up multiple scattered devices on the LAN.
Power over Ethernet provides for the power to be carried on two wire pairs, to comply with safety standards and existing cable limitations. 802.3af power sourcing equipment contains a detection mechanism to prevent sending power to noncompliant devices. Only terminals that present an authenticated Power over Ethernet signature will receive power, preventing damage to other equipment.
The 802.3af specification defines the current delivered to each node in the network as limited to 350 milliamps. The total amount of continuous power that can be delivered to each node, taking into account power loss over the cable, is 12.95 watts. For typical networked devices, such as IP telephones or wireless LAN access points, this is sufficient power because these types of devices consume between 3 and 10 watts of power.
However, other devices, and specifically LAN printers, typically require higher power. For example, LAN printers require additional power to be able to print at high speeds and/or to print images having extensive data. In this instance the total amount of continuous power that is supplied to the printer by the Ethernet connection is insufficient to support high speed printer and/or printing of data intensive materials.
Additionally, other networked devices, specifically LAN printers, typically rely on conventional AC electrical connections as a means of supplying power. However, outages in the AC electrical power routinely occur and interrupt the printing process. In addition to impeding the print process, power outages may cause the loss of data and configurations in the printer control and image generating electronics. The loss of such data and configurations means that once the AC electrical power is restored, the printing process can not resume until the data and configurations are reset in the printer control and image generating electronic. Such resetting of data and configurations further delays printings; thus, adding unnecessary inefficiency to the printing operation.
Some computer peripheral devices, which can be networked or non-networked, are configured to be powered via a Universal Serial Bus (USB), by which the devices can also receive commands or other communications. Standard USB (e.g., the USB 1.1 and USB 2.0 protocols) can be used to power devices but generally provides only low power, typically a maximum power of about 2.5 watts. Devices that require more than about 2.5 watts during operation, such as typical printers, are therefore not powered by standard USB. Instead, such devices are powered by a separate power supply or are configured for a different USB protocol such as powered USB (or “USB PlusPower”), which can typically provide no more than about 48 watts continuously (at 24 volts DC) per connector. A separate power supply typically requires a conventional AC electrical connection, which is subject to possible outages as described above. While a powered USB connection may avoid reliance on a separate conventional AC electrical connection, a powered USB connection may be unavailable in some cases, e.g., where the device is to be connected to a computer that does not have an available powered USB connection.
Therefore a need exists to develop LAN printers, specifically Ethernet LAN printers that are able to benefit from Power over Ethernet specifications, and/or printers that can benefit from power provided via other powered interfaces such as a Universal Serial Bus. The desired printers and methods should provide for adequate power to be supplied to the printer to support high speed printing and/or the printing of data intensive materials. Additionally, the desired printers and methods should provide for interface power such as Ethernet or USB power to sustain printing operations in instances in which outages occur in the main AC electrical connection. In addition to providing back-up power for the print operations, the interface power should provide back-up power to the data and configuration settings in the printer control and image generating electronics, insuring that such information is not lost during an AC power outage. Further, the printers should be adaptable for controlling a printing operation according to the power required for the operation, where the power is supplied by a powered interface or by another power supply.